As electronic communication becomes more widely used, it becomes increasingly important to be able to transmit information with low average power and with a system of modulation that is highly resistant to interference and noise.
The most common technique in present day communications is to employ modulation for superimposing one or a plurality of messages upon a high-frequency carrier, which is then transmitted through a transmission medium and demodulated at a receiving location to recover separately the intelligence contents of the various messages. The message signals in their original form may be audio, data pulses, video, or of some other character. The medium through which the high-frequency carrier passes may be the air, in the case of radio transmission; coaxial cable; optical fiber cable; or other type of medium.
Many engineering factors are important, including among others initial cost, reliability, and useful life of equipment; operating power required; fidelity of transmission; and susceptibility of the transmission to noise or interference. Another factor that enters into present day situations is the need for government approval for radio transmitting equipment. The government has set a standard for average transmitted power above which a separate government license must be obtained for each installation. It is advantageous in many situations to be able to communicate by electronic means without the need for such government approval.
It has been previously known, however, to utilize a method of communication in which only very short, very widely separated pulses of energy are transmitted. That method does hold a promise of lower susceptibility to noise or interference, and may also avoid the need for a government license. It is that type of system to which the present invention relates.